Fix nullable colums for subqueries in left and full joins

internal/compiler/output_columns.go

@@ -359,6 +359,7 @@ func isTableRequired(n ast.Node, col *Column, prior int) int {
 // Return an error if an unknown column is referenced
 func sourceTables(qc *QueryCatalog, node ast.Node) ([]*Table, error) {
 	var list *ast.List
+	var nullableNodes []*ast.Node
 	switch n := node.(type) {
 	case *ast.DeleteStmt:
 		list = &ast.List{
@@ -369,14 +370,29 @@ func sourceTables(qc *QueryCatalog, node ast.Node) ([]*Table, error) {
 			Items: []ast.Node{n.Relation},
 		}
 	case *ast.SelectStmt:
-		list = astutils.Search(n.FromClause, func(node ast.Node) bool {
-			switch node.(type) {
+		dirtyList := astutils.Search(n.FromClause, func(node ast.Node) bool {
+			switch t := node.(type) {
 			case *ast.RangeVar, *ast.RangeSubselect, *ast.FuncName:
 				return true
+			case *ast.JoinExpr:
+				if t.Jointype == ast.JoinTypeLeft || t.Jointype == ast.JoinTypeFull {
+					return true
+				}
+				return false
 			default:
 				return false
 			}
 		})
+		// split result into nullableJoins and list of nodes to handle
+		list = &ast.List{}
+		for i, v := range dirtyList.Items {
+			switch t := dirtyList.Items[i].(type) {
+			case *ast.JoinExpr:
+				nullableNodes = append(nullableNodes, &t.Rarg)
+			default:
+				list.Items = append(list.Items, v)
+			}
+		}
 	case *ast.TruncateStmt:
 		list = astutils.Search(n.Relations, func(node ast.Node) bool {
 			_, ok := node.(*ast.RangeVar)
@@ -413,9 +429,15 @@ func sourceTables(qc *QueryCatalog, node ast.Node) ([]*Table, error) {
 
 		case *ast.RangeSubselect:
 			cols, err := outputColumns(qc, n.Subquery)
+
 			if err != nil {
 				return nil, err
 			}
+			if astutils.IsChildOfNodes(nullableNodes, &item) {
+				for _, c := range cols {
+					c.NotNull = false
+				}
+			}
 			tables = append(tables, &Table{
 				Rel: &ast.TableName{
 					Name: *n.Alias.Aliasname,

internal/endtoend/testdata/join_left/postgresql/query.sql

@@ -111,3 +111,14 @@ FROM    users_2 u
             ON u.user_avatar_id = m.media_id
 WHERE   u.user_id != @user_id
 LIMIT   @user_imit;
+
+-- name: GetMayorsOptionalInnerSelect :many
+SELECT t1.user_id, t2.full_name
+FROM (
+    SELECT user_id, city_id FROM users WHERE users.city_id = $1 LIMIT 1 OFFSET 0
+) AS t1
+LEFT JOIN cities on t1.city_id = cities.city_id
+LEFT JOIN (
+    SELECT mayors.mayor_id, mayors.full_name
+    FROM mayors where mayors.mayor_id = $2
+) AS t2 on t2.mayor_id = cities.mayor_id;

internal/sql/astutils/search.go

@@ -19,3 +19,25 @@ func Search(root ast.Node, f func(ast.Node) bool) *ast.List {
 	Walk(ns, root)
 	return ns.list
 }
+
+func IsChildOfNodes(parents []*ast.Node, node *ast.Node) bool {
+	for _, v := range parents {
+		if IsChildOfNode(v, node) {
+			return true
+		}
+	}
+	return false
+}
+
+func IsChildOfNode(parent *ast.Node, node *ast.Node) bool {
+	res := Search(*parent, func(n ast.Node) bool {
+		if n == *node {
+			return true
+		}
+		return false
+	})
+	if len(res.Items) > 0 {
+		return true
+	}
+	return false
+}